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Modélisation et analyse de services éco-hydrauliques des réseaux de canaux et fossés des agrosystèmes méditerranéens

Abstract : Agroecological infrastructures are semi-natural landscape elements providing ecosystem services and disservices. In Mediterranean agrosystems, ditches and irrigation channels provide eco-hydraulic services relying on interactions between vegetation and water, sediments and plant propagules (seeds) transport. Management operations aiming at restoring the hydraulic capacity of these infrastructures are likely to modify the expression of these services. However, the interactions between practices, vegetation cover traits and ecosystem services provided by these infrastructures are still poorly characterized. The objective of this work was to understand in which extent ditch and channel management regimes, in terms of typology, but also in terms of temporality and location, influence eco-hydraulic services provided by vegetation.The approach relies on the development of a model proposing an explicit representation of the hydraulic network which functioning is simulated for reference events on the considered time horizon. The model is based on semi-empirical formalisms taking into account the effect of plant traits on transport processes, and especially their dynamical effect on hydraulic resistance. It was parameterized based on field experiments made in two Mediterranean agricultural study areas. These experiments aimed at : (i) characterizing the influence ofdifferent geomorphological factors and management regimes in the spatial distribution of ditch plant communities and their traits (ii) identifying the factors implied in the transport and deposition of propagules during an hydraulic event.The experimental results show that management regimes influence the dynamics of the vegetation cover at short-term, but that the spatial distribution of species (and therefore traits of the vegetation cover) is largely associated with geomorphological factors. They helped to improve our understanding of major key-processes of agricultural channel networks, especially propagules dispersal, and to propose a methodology for the relocation of the propagules in intermittent waterways. The spatialized model, integrating the main experimental results atthe catchment scale, enabled a ranking of the impact of practices regarding the bundle of services provided by agricultural ditches’ vegetation. Mowing provides the best trade-off between services in the short and medium term, although it is temporarily unfavourable for sediments and seeds retention, aswell as for bank stabilization, at the beginning of autumn. The developed semi-empirical approach gives the opportunity to question the level of description of processes and required indicators for services evaluation in complex ecosystems.
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Gabrielle Rudi. Modélisation et analyse de services éco-hydrauliques des réseaux de canaux et fossés des agrosystèmes méditerranéens. Agriculture, économie et politique. Montpellier SupAgro, 2019. Français. ⟨NNT : 2019NSAM0007⟩. ⟨tel-02524515⟩

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